Lesson 3 - Token Ring and SNAP

   Introduction

This lesson covers the SNAP frame format as seen in Ethernet as well as Token Ring networks that use IEEE 802 protocols, such as 802.3 and 802.5. SNAP allows the newer IEEE 802 style frames to carry a Version 2 Type field. Remember, the Type field is 2 bytes long and holds many values that cannot be expressed in a 1-byte DSAP field, such as found in the LLC header. The format of an 802.5 Token Ring frame is also discussed in this section.

   Objectives

At the end of this lesson you should be able to:

1.	Describe the format of a Token Ring frame
2.	Understand the purpose of a Subnetwork Access Protocol (SNAP) header
3.	Describe the format of a SNAP-encoded frame

Key Point
The SNAP format allows a Type field to be carried by an IEEE 802 style frame.

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